Current emission regulations relating to NOx require reciprocating engines to operate at very lean fuel/air mixtures. The excess air keeps the combusting gases cooler and limits thermal NOx development. At the same time, the lean mixture requires much more energy to be delivered to the spark plug for successful ignition. The higher energy flowing through the spark plug electrodes increases erosion to the point that the spark plugs last only hundreds of hours. The spark plugs also cost in excess of $100 each because of the rare earth metals used in the electrodes to extend their life. The resulting maintenance costs are thus very high, especially for natural gas fueled energy generation engines which must run continuously for thousands of hours.
The concept of delivering peak energy with fiber optics has received much attention in this regard. However, when energy sufficient to generate a plasma pulse is directed through an optical fiber, the fiber and spot size must be large to prevent fiber destruction. The large fiber size dictates the size of the exit aperture, with a large exit aperture making it difficult to focus the light to a sufficiently small diameter to generate a plasma spark. It is possible to deliver enough energy for a spark when focused on a condensed material, but not for the gas phase. What is desired is to transmit the light through a small diameter, single mode fiber. However, when the energy is focused to a small enough diameter to match the smaller fiber size, it usually generates a spark prior to entering the fiber, or impurities in the fiber cause the fiber to fracture with the high power, in either case rendering the optical fiber useless.
Therefore, there is a need for a low cost and efficient laser spark system, for use in various applications such as reciprocating engines, turbine combustors, explosives, destruction or overloading of electronic imaging devices, and laser induced breakdown spectroscopy diagnostic sensors.